1. Field of the Invention
The present invention relates to an enhanced arrangement for supplying continuous power to a circuit board, and in particular, to an enhanced arrangement for supplying continuous power to a circuit board disposed in drawer, using a movable buss bar and a feed-through connector.
2. Background Information
Backplanes are wiring boards used, for example, in computers, and are typically provided with card slots or plugs for receiving various circuit boards, such as a processor card and a so-called memory riser card, attached to a common surface of the backplane by way of the card slots or the plugs. The circuit boards and backplane typically have various electrical components located thereon (for example, the Dual In-Line Memory Modules (DIMMs) on the memory riser card), which tend to consume a substantial amount of electrical power. In order to supply the electrical components with power, it is conventional to electrically connect the backplane to an external power supply. The backplane then distributes the power received from the external power supply to the appropriate electrical components in a known manner.
In order to connect the backplane to the external power supply, it is conventional to utilize a buss bar (also known as a busbar or bus). A buss bar is typically a heavy, fixed, rigid, metallic conductor, used to carry a large current and/or to make a common connection between several circuits. The buss bar can be configured to both transmit power from the external power supply to the backplane, and serve as a ground for the backplane. Alternatively, separate buss bars may be provided, with one or more of the buss bars being used to transmit the power, and one or more further buss bars being used as a ground. The advantages of using a buss bar, as opposed to using a number of individual power transmission wires or cables, are well known to those skilled in the art. Such advantages include, for example, reduced resistance (a high resistance may disadvantageously lead to voltage swings due to current fluctuations), an organized power transmission scheme due to the elimination of the power transmission wires or cables, and a reduction in undesirable electrical noise, which may be generated when using a number of individual power transmission wires or cables.
Often, it may be desirable to access the circuit boards and/or the backplane, in order to perform system maintenance or to upgrade the computer. For example, it is conventional to remove a circuit board from the computer so that various electrical components thereon can be replaced or added to.
Further, the current trend is to make computers smaller, and hence less costly. In order to reduce the overall size of the computer, the circuit boards and backplane are packaged tightly together, thus reducing accessibility to the various components disposed thereon.
In order to provide access to the circuit boards and backplane for maintenance and upgrading, it is known to space the various circuit boards apart from each other. Although this allows more room for a technician to grasp a respective circuit board, this also disadvantageously results in an increase in size of the computer.
Alternatively, it is also known to arrange the circuit boards in an accessible location, for example, at a top of the computer. The various circuit boards can then be accessed through a removable access door disposed at the top of the computer. However, this arrangement disadvantageously prevents a stacking of computers on top of each other.
A further known configuration includes placing the backplane and circuit boards inside of a slidable drawer. When access to the backplane or circuit boards is needed, the technician merely slides the drawer open, thus allowing the various boards to be removed.
However, typically the power supply is disposed external to the drawer, due to its considerable size. Thus, connecting the backplane (which is disposed in the movable drawer) to the external power supply using a conventional rigid buss bar is problematic. That is, in order to electrically couple the conventional buss bar to the backplane, a plug-type buss bar connector may be provided, which is coupled to the backplane, for example. The plug-type buss bar connector allows the buss bar, which is coupled to the power supply, for example, to be plugged to the backplane. When the drawer is in a closed position, the buss bar has one end plugged into the plug-type buss bar connector, and another end coupled to the power supply, for example. This allows power to be supplied to the backplane via the buss bar and the connector. When the drawer is slid to an open position, the connector is moved out of engagement with the buss bar, thus interrupting the supply of power to the backplane.
However, users of many computers require their computers to remain operational at all times. That is, it is now desirable to be able to perform so-called "concurrent maintenance", i.e., maintenance that is performed without powering down the various boards of the computer. It is additionally desirable to be able to perform system upgrades while the various boards are supplied with power, i.e., the "hot plugging" of circuit boards and components. In order to accomplish this, it has been necessary to electrically couple the mother board (backplane) to the external power supply using flexible cables, rather than using a buss bar. However, as noted above, the high electrical resistance of a cable can cause voltage fluctuations due to current variations. On the other hand, wide voltage swings cannot be tolerated, since the components disposed on the various circuit boards may operate at a relatively low voltage. As such, voltage regulators are typically provided. However, using a voltage regulator in this manner disadvantageously increases the cost of the overall system. Further, power supplies in today's systems are typically limited to the power provided at the line (i.e., 20 amps, 110 volts). With system power requirements growing, and with the source of power being limited, it is desirable to increase the transforming efficiency of a power supply. However, the use of voltage regulators reduces the overall efficiency of the power regulation of the system. Thus, there is a need for a buss bar that will allow for the continuous transmission of power to the circuit boards disposed in a drawer, even when the drawer is open, thus eliminating the requirement for additional voltage regulators.
Additionally, in order to provide an efficient transfer of power, it is preferable if the buss bar is engaged with the backplane using a buss bar connector. Buss bar connectors are tailored to provide a large number of A-spots at the point of engagement with the buss bar. An A-spot is the point of contact between adjoining surfaces. Because all surfaces are defined (on a microscopic level) by a plurality of peaks and valleys, when two such surfaces are placed in contact with each other, the two surfaces will only be in contact with each other at the highest of the peaks. Further, it is generally assumed that only one A-spot can be ensured between any two adjoining surfaces, i.e., at the point where the highest peak on either of the two surfaces contacts the other surface. As will be appreciated, this point of contact is typically quite small, with the size of the A-spot being dependent on the hardness of the two contact materials, and the contact force between the two contact materials. As the hardness of the materials increases, the size of the A-spot will decrease. Inversely, as the contact force between the two contact materials increases, the size of the A-spot will increase.
Since current can only flow from one conductive material to another adjacent conductive material at the A-spots, it is apparent that a larger A-spot will advantageously have a lower resistance, thus allowing the current to pass from one material to another more freely. Similarly, increasing the number of A-spots between two conductors will effectively reduce the resistance therebetween, thus also allowing the current to pass more freely. The conventional buss bar connectors provide for a relative large number of A-spots that will engage with a buss bar at a relatively high contact force, thus ensuring adequate electrical coupling is achieved between the buss bar and the backplane.
However, the conventional plug-type buss bar connector described above does not allow a feed through arrangement of the buss bar. In particular, the conventional plug-type buss bar connector is configured to only allow the buss bar to be inserted partially therein, thus precluding its use in an arrangement where the backplane is disposed in a drawer, and continuous power is desired (i.e., when the drawer is open, the buss bar will be unplugged from the connector). However, the elimination of a buss bar connector may prevent an adequate electrical interface from being established between the buss bar and the backplane. Thus, there is a need for a buss bar connector that will allow for a feed through connection to a buss bar.